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Mir, Ubuntu's in-progress replacement for the X Window System, is being used internally at Ubuntu developer Canonical and will be available to all users in the next version of the operating system. Mir was announced in March, with Canonical saying that a new display server is needed to power the Unity interface across desktops, phones, and tablets.

"Mir has been running smoothly on my laptop for two weeks now," Canonical founder Mark Shuttleworth wrote on his blog yesterday. While he provided no statistics, he wrote that "Xorg and Compiz are using less memory and fewer CPU cycles under Mir than they were with X handling the hardware directly."

Shuttleworth did list one downside, however: "Chromium triggers an issue in the graphics stack which freezes the display. Pressing Alt-F1 unfreezes it (it causes Compiz to invoke something which twiddles the right bits to bring the GPU back from its daze). I’m told that will get sorted trivially in a coming update to the PPA [Personal Package Archives, Ubuntu's software repository]."

According to the Mir roadmap, Canonical hopes to completely replace X on desktops and laptops by October when Ubuntu 13.10 is released, but the OS will still feature a "legacy mode" that can "run legacy X clients against an on-demand rootless X server." Mir will also be able to "support an Ubuntu phone product" in October. By April 2014, Mir will power all Ubuntu form factors, including tablets.

Shuttleworth wrote that Canonical developers are now busy making sure that every app and desktop environment will work well under Mir.

"On Ubuntu, we’re committed that every desktop environment perform well with Mir, either under X or directly," Shuttleworth wrote. "We didn’t press the ‘GO’ button on Mir until we were satisfied that the whole Ubuntu community, and other distributions, could easily benefit from the advantages of a leaner, cleaner graphics stack." Distributions based on Ubuntu will be able to offer Mir as an option with a patch to X.

For people who want to try Mir before its official release, it will be available in beta versions of 13.0 through the Ubuntu PPA "just as soon as our QA and release teams are happy that its ready for very widespread testing," Shuttleworth wrote.

According to Ubuntu's roadmap, they will be running X on top of Mir for the next two releases (13.10 and 14.04LTS), which means that X11 and the current version of Unity built on Compiz will be supported at least 5 more years. The upcoming release is expected to run Mir for users with open source video drivers, and the LTS is expected to run Mir (with an X server) for everyone with no legacy X.org fallback.

The Mir native Unity rewrite in Qt 5 is planned to debut in October 2014. Canonical is patching in Mir support to most of the common GUI libraries ( Qt, Gtk+, Gecko), but it is not clear whether the all the upstream projects will accept these patches. This is where we might see some of the Ubuntu spins going in a different direction.

It seems like a reasonable 2-step strategy to replace the back-end before changing the client protocol, and it keeps the most disruptive changes from landing in the 14.04 LTS window. As Matty says, it's the huge revolution it sounds like in the Ars article or from a naive reading of the Shuttleworth blog, but it is an important step in a fairly conservative transition strategy.